The present invention relates to a continuously operable sugar centrifuge wherein centrifuging channels including outwardly facing screen walls are arranged on the circumferential surface of a conical frustum rotatable about a central rotational axis. Passage means lead into the channels for supplying wash and/or coating mediums to the massecuite which reaches the screen surface.
Different kinds of continuously operable or operating sugar centrifuges are well known in the art. Known centrifuges of this type generally operate in accordance with the so called thin layer principle, whereby the massecuite is distributed in thin layers onto a centrifuging screen drum. The screen drums have a conical frustum shape and the screen proper is secured to the inside of the frustum. The operational conditions of known centrifuges of this type are adjustable. One adjustment may be made with regard to the rotational speed of the centrifuge. Another adjustment may be made with regard to the angle of inclination of the screen surface relative to the rotational axis of the centrifuge. Thus, the operational conditions may be adjusted in such a manner that the massecuite which is supplied to the screen drum at the smaller diameter end of the drum forms a uniform thin layer over the entire screen surface. Such thin layer travels with a predetermined speed along the screen surface toward the discharge end located at the larger diameter end of the centrifuge jacket. During this travelling of the massecuite along the screen the liquid present in the massecuite is first centrifuged out of the massecuite. The wash or coating liquid, which is later supplied to the crystal layer, is centrifuged in the same manner to clear or free the crystals from any liquid remainders of the massecuite still sticking to the crystals.
Past experience has shown that so far it has not been possible to use these continuously operating or operable centrifuges for producing satisfactorily white sugar from so called A-type massecuite. This type of massecuite yields white sugar which does not require any further treatment in its production.
One reason for these difficulties is seen in that, according to experience, thin layers of sugar crystals do not yield a satisfactory washing. Another difficulty is seen in that the removal of the sugar crystals from the continuously operating centrifuge results in a substantial proportion of crystal breakage. So far it has not been possible to avoid such crystal breakage in spite of many efforts to solve this problem.
On the other hand, it is not possible to use thicker sugar crystal layers in continuously operating centrifuges of the known type because thicker layers tend to shift on top of each other in the conical drum during the centrifuging. Such shifting of the crystal layers reduces the quality of the centrifuging result whereby the efficiency as well as the sugar quality is reduced. Yet another drawback is seen in that the thicker layers may cause unbalances of the rotating drum which places undesirably heavy loads on the drum bearings thereby creating well known disadvantages and dangers.